Device for fixation of bone fractures

ABSTRACT

A medical assembly is provided for the positive fixation of fractures of the ulna, one of the forearm bones, in cases where it is broken at or near the elbow joint. One element of the assembly is secured to the distal (remote from the body) part of the ulna, and another threaded element is independently tightened up to impact the bone fragments. The first element may be a metal element or unit inserted from the side through the cortex, or hard outer part of the forearm bone, below the break. This metal element, referred to as the cortical fixation unit, extends into the soft center channel of the bone and has a transverse threaded hole near its end, opening to the center channel of the bone. The other element may be a flexible bolt or pin formed of a threaded stiff wire about six inches long having a bolt head at one end, and will be referred to as a &#39;&#39;&#39;&#39;pin&#39;&#39;&#39;&#39; in the present specification. This flexible bolt or pin is pushed through a drilled hole in the elbow fragment of the bone, down the bone channel and engaged with the threaded hole at the end of the cortical fixation unit. By tightening up the bolt head on the flexible bolt or pin, the elbow fragment is positively set in its proper position in engagement with the remaining distal portion of the ulna.

United States Patent [19:

McAtee [4 Oct. 9, 1973 DEVICE F OR FIXATION OF BONE FRACTURES [76]Inventor: Richard M. McAtee, 355 South G St, Oxnard, Calif. 93030 [22]Filed: V Mar. 15, 1972 [21] Appl. No.: 234,849

Primary Examiner-Richard A. Gaudet Assistant Examiner-J. YaskoAttorney-Alan C. Rose [5 7 ABSTRACT A medical assembly is provided forthe positive fixa tion of fractures of the ulna, one of the forearmbones, in cases where it is broken at or near the elbow joint. Oneelement of the assembly is secured to the distal (remote from the body)part of the ulna, and another threaded element is independentlytightened up to impact the bone fragments. The first element may be ametal element or unit inserted from the side through the cortex, or hardouter part of the forearm bone, below the break. This metal element,referred to as the cortical fixation unit, extends into the soft centerchannel of the bone and has a transverse threaded hole near its end,opening to the center channel of the bone. The other element may be aflexible bolt or pin formed of a threaded stiff wire about six incheslong having a bolt head at one end, and will be referred to as a pin inthe present specification. This flexible bolt or pin is pushed through adrilled hole in the elbow fragment of the bone, down the bone channeland engaged with the threaded hole at the end of the cortical fixationunit. By tightening up the bolt head on the flexible bolt or pin, theelbow fragment is positively set in its proper position in engagementwith the remaining distal portion of the ulna.

8 Claims, 6 Drawing Figures 1 DEVICE FOR FIXATION OF BONE FRACTURESBACKGROUND OF THE INVENTION This invention relates to an improvedmedical assembly for the fixation and impaction of bone fragments.

The principal bones in the arm include the upper arm bone, or humerus,and the two forearm bones, the ulna which is the bone having its loweror distal end alined with the smallest finger of the hand, and theradius which has its distal end alined with the thumb. The elbow jointincludes a crescent-shaped recess in the ulna and a correspondingmatching convex surface at the lower end of the humerus.

The medical term for the crescent-shaped recess is the semi-lunar notch,and the enlarged end of the ulna at the elbow is called the olecranon.The medical convention of referring to the end of a bone closest to thebody as the proximal" end, in constract to the distal" or farther endwill be followed in this specification.

When the ulna is broken near its proximal end, at or close to thesemi-lunar notch, the triceps muscles tend to pull the bone fragmentupward away from the main distal portion of the bone and it is difficultto set the bones in their proper relative positions for mending.

It has previously been proposed to use a sort of screw which extendsthrough a hole drilled in the end of the bone fragment and which isprovided with screw threads which are directed into the soft centerchannel, known as the medullary canal, of the main distal portion of theulna. However, this procedure does not always accommodate different boneshapes and sizes and types of breaks. More specifically, it is notalways possible to have the screw reach the desired tightness just asthe head of the screw brings the bones into the properly set or reducedposition, without repeated insertions and removals of the screw, eitherwith modifications, or using a different length screw.

It has also been proposed to set the ulna bone fragments, or reduce thefracture, by using metal wires or plates or absorbable material such ascatgut, kangaroo tendon or the like. However, such techniques arefrequently complicated by the pull of the triceps muscles, which arelocated on the back of the humerus, or upper arm bone. These tricepsmuscles normally pull on the olecranon or upper end of the ulna toextend the forearm. When the ulna is broken near the elbow, the upper ordistal bone fragment is pulled upward, away from its normal position, bythese powerful triceps muscles.

In view of the problems of reducing the fracture against the force ofthe triceps muscles, it has also frequently been proposed to completelyexcise or remove the broken bone fragment near the elbow. However, thiswidely used technique gives rise to severe instability of the joint anda decrease in triceps power, and has many disadvantages as can readilybe appreciated.

SUMMARY OF THE INVENTION Against the foregoing background, the presentinvention contemplates securing a metal element or cortical fixationunit into the main lower or distal portion of the ulna, and the screwingin of another member (relative to the cortical fixation unit) whichbears on the olecranon to hold the bone fragments firmly in placeagainst the strong pull of the triceps muscles.

As set forth in the Abstract of the Disclosure," a first hole ispreferably drilled transversely through the cortex, or hard outer wall,of the main part of the ulna into the soft medullary channel. Anotherhole is drilled through the olecranon at the upper end of the elbow bonefragment. The cortical fixation unit is pushed through the first hole inthe cortex, this unit being provided with a transverse threaded holealined with the medullary channel. A long flexible threaded wire or pinis then inserted through the hole in the olecranon, down the medullarycanal and into the threaded hole in the short transverse corticalfixation unit, and the pin is tightened up until it impacts the bonesfirmly and properly secures the bone fragments together.

The method has the advantage of providing easily adjustable impaction ofthe fragments of the broken bone, in a positive way against theseparating force of the triceps muscle, and independent of the problemof securing the assembly to the main distal portion of the ulna.

Other advantages and features of the invention will become apparent fromthe following detailed description and from the drawings, in which:

FIG. 1 is a drawn fron an X-ray to show relative bone positionsfollowing a fracture of the upper end of the ulna;

FIG. 2 shows the ulna with the broken bones set or reduced, inaccordance with the principles of the invention;

FIGS. 3 and 4 are two views of the cortical fixation unit having athreaded hole, which is one part of the assembly;

FIG. 5 is a side view of the elongated threaded wire, or flexible pin,and the cortical fixation unit, which are used as shown in FIG. 2; and

FIG. 6 shows a holder which is used in inserting the unit shown in FIGS.3 and 4 into a position such as that shown in FIG. 2.

Referring more particularly to the drawings, FIG. 1 is taken from anX-ray of the elbow region taken following a fracture of the ulna 12 nearthe elbow. The bone fragment 14 is in engagement with the humerus, orupper arm bone 16. The other forearmbone 18, the radius, is shown abovethe ulna 12.

The triceps muscle on the back of the upper arm is secured through atendon to the upper or proximal end of the ulna. The force applied tothe upper end of the ulna bythe triceps must be powerful, in view of theshort moment arm" or distance from the end of the elbow to the effectiveturning point of the ulna.

This powerful force of the triceps pulls the bone fragment 14 up to theindicated position, and exerts a continuing force on the bone fragmenttending to pull it away from the remainder of the ulna 12 when the bonesare set. The present invention is directed to the solution of thisproblem.

FIG. 2 shows the ulna in greater detail, and also shows the assembly forfixation of the fracture. In FIG. 2 the ulna 12 of a left arm is shownwith the distal end 20 to the right and the proximal end to the left.The ulna 12 is fractured along a break 22 extending to the semi-lunarnotch 24, with the bone fragment l4 including the olecranon or elbowprotruberance 25 of the ulna.

The assembly for fixation of the fracture includes a cortical fixationunit 32, provided with a threaded transverse opening 34 (as shown inFIG. 3), and a long flexible bolt or threaded pin 38 having a bolt head40,

and a washer 42. The mode of insertion of the fixation assembly will beset forth in some detail below.

FIGS. 3 and 4 are side and top views, respectively, of the corticalfixation unit 32. It is provided with a tapped hole 34 near one end. Theother end is provided with a head 36 of a configuration which canreadily be mechanically held, and which will indicate alinement with thetapped hole 34. As shown in FIG. 4, the head 36 has two flat sidesalined with opening 34 and a central recess for use with the holdingdevice shown in FIG. 6. The shank of the cortical fixation unit 32 mayhave a diameter of 0.200 inch, and it may be about twenty three-sixtyfourths inch in length, although an assortment of lengths are desirablefor use with different bone dimensions.

The long flexible medullary (or marrow) pin is shown in the assemblyview of FIG. 5. The shank of the pin may be three-thirty seconds indiameter, and it is provided with threads starting about I 1% inchesfrom its head which may bave a pitch of 48 turns per inch. These threadsshould match those in the threaded hole 34 in the cortical fixation unit32, of course. To facilitate starting the threads of the flexible pin 32in the threaded hole 34, the end of the medullary pin 32 is providedwith a rounded and slightly tapered unthreaded end portion 44 of reduceddiameter which is about one-fourth inch long or slightly longer toextend through the threaded hole 34 in the cortical fixation unit andproperly aline the parts. With this arrangement, problems in startingthe threading where the threaded hole is not visible, are minimized.

The washer 42 serves to avoid abrasion and facilitate tightening of themedullary pin 38 as the hexagonal head 40 is tightened.

FIG. 6 is a cross-sectional view of a simple holder 52 for the corticalfixation unit 32. The holder 52 includes two parts 54 and 56 which maybe longitudinally adjusted to engage the cortical fixation unit 32 byrelative rotation about threads 58. The part 56 has two fingers 60 and62 which extend around the flat sides of the head 36 of the corticalfixation unit 32; and the other part 54 of the holder 52 has a pointedcentral shaft 64 which engages the recess 37 in the head of the unit, topositively hold it in place.

In FIG. 2, the position of the fixation device or assembly 32, 38 isshown relative to the fractured ulna. The medical procedure for applyingthe assembly will now be briefly set forth.

After standard preparation for an arm operation, a posterior incision ismade at the elbow in the usual manner, curving the incision slightlytoward the lateral side at the olecranon bursa, to avoid injuring thebursa (which permits freedom of movement of the skin over the elbow).Over the distal fragment the incision is carried through the periosteum(or covering of bone), then' the bone is exposed by subperiostealdissection approximately three quarters of an inch distal to thefracture site. Care is taken to remove all small fragments of bone andtissue tags that may invert into the fracture site. The lateral andmedial aspects of the fracture site are adequately exposed to detect anyfrag ments which may prevent adequate approximation (or pulling togetherof the bones). A towel clip (or clamp) is then placed through the tendonof the triceps proximal to the olecranon and in this manner the proximalfragment can be easily controlled while reducing the fracture. Thefracture is reduced carefully.

A small cruciate incision is made through the triceps tendon at the tipof the olecranon and a hole is drilled through the olecranon, alinedwith the marrow canal of the ulna. The drill hole should be aboutnine-sixty fourths inch in diameter size to avoid any possible bindingof the flexible medullary pin (preferably of threethrity seconds inchdiameter) in the olecranon fragment. The medullary pin 32 is firstassembled with the washer 42 and is then driven through the drill holein the olecranon and into the marrow canal with a gentle tap of amallet.

A second incision is made over the shaft of the ulna an inch to twoinches distal to the fracture site. By subperiosteal dissection theflexor surface of the ulna is exposed. (The flexor side of the forearmis the inner surface which continues into the plam of the hand.) At thislevel the cross section of the ulna is triangular in shape and theflatter surface is on the flexor aspect. A onequarter inch hole isdrilled through the flexor surface of the ulna entering into the marrowcanal. The hole is drilled through the marrow, and a few millimetersinto the opposite cortex (the hard outer part of the bone).

When the tip 44 of the medullary pin 38 is seen through the lateraldrill hole, the tip is withdrawn slightly so that the cortical fixationunit 32 can be placed in the hole and with its threaded hole 34 alinedwith the tip of the medullary pin. Technically, this is the moredifficult part of the procedure, but it is made eas ier if one choosesthe unit 32 of the right length, and if the drill hole into the oppositecortex is adequate to allow some leeway in manipulation of the fixationunit 32. Once they are joined, the smooth section on the tip 44 of themedullary pin slides into the threaded hole in the unit 32, alining thethreads accurately. A small socket wrench fitted to a handdrill is themost convenient instrument for threading the flexible medullary pin 38through the hole 34 in the unit 32 and down the shaft of the ulna. Thisgives very positive control in approximating the fragments, and almostany desired degree of impaction can be accomplished in this manner. Ifthe fracture line is oblique the fragments tend to override withimpaction. This distortion can be prevented by holding the fracturereduced and then inserting a Kirschner wire across the fracture siteparallel to the pin. The fragments are then impacted by tightening theflexible medullary bolt while the more rigid Kirschner wire keeps thebone fragments alined. The wounds are closed in the usual manner and thearm is dressed with gentle compression. A posterior molded splint isapplied for patients comfort during the first several post-operativedays. After wound healing and removal of the sutures, gentle activemotion is begun. Other circumstances such as extensive comminution, lossof fragments of bone, or other fractures about the elbow or forearm maymitigate against early motion.

Concerning other aspects of the invention, it is of course necessarythat the fixation assembly be made of biologically inactive material. Anumber of materials are used for this purpose in surgical implant workand one such material, a stainless steel, is identified as ASTMDesignation: F55 and is made of iron alloyed with the following metalsin the indicated quantities:

Chromium HBO-20.00% Nickel l0.00-l4.00% Molybedenum ZOO-4.00%

The following metals shall not be present in excess of the followinglevels:

Carbon 0.08% Max. Manganese 2.00% Max Phosphorus 0 03% Max Sulfur 0.03%Max Silicon 0.75% Max.

The arrangements described in detail above in connection with thedrawings represent the preferred mode of implementing the presentinvention. It is useful, however, to consider alternative arrangementswhich would. realize many of the advantages of the preferredarrangements. Broadly from one aspect, the invention contemplates firstsecuring one part of the bone fixation assembly against longitudinalmovement relative to the main distal portion of the ulna, and then in asecond step exerting fixation force on the olecranon bone fragment.

These two steps can be implemented in a number of ways, including anassembly similar to that used in bicycle wheels. Using this concept,holes would be drilled in the two bone fragments similar to thosediscussed hereinabove. But instead of the unit 32 as shown in FIGS. 3and 4 of the drawings, a curved cortical fixation element having a headand a central threaded aperture would be employed, similar to those usedto secure bicycle spokes in place. This curved element would be insertedin the lateral hole in the distal part of the ulna, with the curved endpointing toward the elbow fragment, so that a flexible medullary boltcould be threaded into it.

Another technique would be to use a semi-flexible medullary screwthreaded on its front end to engage the inner surface of the ulna, andthreaded on its other end to engage matching threads on a nut. Themedullary screw could be provided with a slot for rotationaldriving,-with the drilled hole through the olecranon being oversize topermit clearance. After the flexible medullary screw is seated in thedistal portion of the ulna, a washer and a nut would be threaded to theother (exposed) end of the screw for fixation, and the extra length ofscrew threads protruding from the olecranon would subsequently be cutoff.

Components serving the function of nuts or other internally threadedelements are sometimes formed in various ways to provide a ratchet-likeaction so that assembly with a bolt or notched member is facilitated inthat, for assembly in one direction, rotation of the bolt is notrequired. Such elements could of course be employed in place of theinternally threaded elements described hereinabove.

The various described embodiments including the foregoing alternativesare all considered to provide advantages over prior methods byseparating the steps of first, securing the bone fixation assemblyagainst longitudinal movement, and secondly, impacting the bonefragments and firmly securing them together. However, the describedalternatives to the preferred method have mechanical complexities andprocedural steps which make them less attractive than the preferredmethod disclosed in detail herein.

What is claimed is:

1. An assembly for the fixation and impaction of a bone fragmentrelative to the main part of a fractured bone comprising:

a first structurally rigid unitary member of biologically inactivematerial including means for engagement with and prevention oflongitudinal movement of said first member relative to the main part ofthe broken bone, said first member also being provided with meansengaging another member of the assembly;

means including a second structurally rigid unitary member ofbiologically inactive material, for entering locking engagement withsaid first engaging means upon relative movement of said members, andfor applying force to a bone surface of the bone fragment to firmly andpositively impact the fractured bone surfaces; and

both said first and second members having enlarged portions for bearingon the exterior surface of the bone at one of their respective ends andhaving mutually locking engagement 'means of reduced size near theirother ends, whereby the two members can be manipulated from outside ofthe bone into direct locking engagement with each other within the bone.

2. A bone fixation assembly primarily for fractures of the upper ulnacomprising:

a first member of biologically inactive material including means forengagement with and prevention of longitudinal movement relative to thedistal portion of the ulna, said first member being provided with afirst set of threads;

means including a second member of biologically inactive material havingthreads engaging said first set of threads, for applying force to theupper end of the bone surface of the olecranon to finnly and positivelyimpact the fractured bone surfaces; and

said first member being a cortical fixation unit having a head bearingon the outer surface of the bone and a hole engaging the second memberwithin the medullary canal of the bone.

3. A bone fixation assembly as defined in claim 2, wherein said firstmember is a short cortical fixation unit having a head for bearing onthe outer surface of the ulna at one end, and a threaded hole near itsother end.

4. A bone fixation assembly'as defined in claim 3 wherein the secondmember is an elongated flexible medullary pin having external threadsmatching the internal threads of said threaded hole at one end, and ahead at its other end.

5. A bone fixation assembly as defined in claim 4 wherein said pin has arounded end of reduced crosssection less than the internal diameter ofthe threaded hole for starting threaded engagement with said corticalfixation unit.

6. A bone fixation assembly as defined in claim 3 wherein the head ofthe cortical fixation unit is asymmetric and indicates the orientationof said threaded hole.

7. A bone fixation assembly as defined in claim 6 wherein the head ofsaid cortical fixation unit has two flat sides for engagement by aholding device and for designating the orientation of said threadedhole.

8. A bone fixation assembly as defined in claim 4 wherein said assemblyfurther includes a washer of biologically inactive material on said pinadjacent the head of said pin to transmit force to the olecranon alongthe axis of said pin as said pin is tightened up.

1. An assembly for the fixation and impaction of a bone fragmentrelative to the main part of a fractured bone comprising: a firststructurally rigid unitary member of biologically inactive materialincluding means for engagement with and prevention of longitudinalmovement of said first member relative to the main part of the brokenbone, said first member also being provided with means engaging anothermember of the assembly; means including a second structurally rigidunitary member of biologically inactive material, for entering lockingengagement with said first engaging means upon relative movement of saidmembers, and for applying force to a bone surface of the bone fragmentto firmly and positively impact the fractured bone surfaces; and bothsaid first and second members having enlarged portions for bearing onthe exterior surface of the bone at one of their respective ends andhaving mutually locking engagement means of reduced size near theirother ends, whereby the two members can be manipulated from outside ofthe bone into direct locking engagement with each other within the bone.2. A bone fixation assembly primarily for fractures of the upper ulnacomprising: a first member of biologically inactive material includingmeans for engagement with and prevention of longitudinal movementrelative to the distal portion of the ulna, said first member beingprovided with a first set of thReads; means including a second member ofbiologically inactive material having threads engaging said first set ofthreads, for applying force to the upper end of the bone surface of theolecranon to firmly and positively impact the fractured bone surfaces;and said first member being a cortical fixation unit having a headbearing on the outer surface of the bone and a hole engaging the secondmember within the medullary canal of the bone.
 3. A bone fixationassembly as defined in claim 2, wherein said first member is a shortcortical fixation unit having a head for bearing on the outer surface ofthe ulna at one end, and a threaded hole near its other end.
 4. A bonefixation assembly as defined in claim 3 wherein the second member is anelongated flexible medullary pin having external threads matching theinternal threads of said threaded hole at one end, and a head at itsother end.
 5. A bone fixation assembly as defined in claim 4 whereinsaid pin has a rounded end of reduced cross-section less than theinternal diameter of the threaded hole for starting threaded engagementwith said cortical fixation unit.
 6. A bone fixation assembly as definedin claim 3 wherein the head of the cortical fixation unit is asymmetricand indicates the orientation of said threaded hole.
 7. A bone fixationassembly as defined in claim 6 wherein the head of said corticalfixation unit has two flat sides for engagement by a holding device andfor designating the orientation of said threaded hole.
 8. A bonefixation assembly as defined in claim 4 wherein said assembly furtherincludes a washer of biologically inactive material on said pin adjacentthe head of said pin to transmit force to the olecranon along the axisof said pin as said pin is tightened up.